In the early 80s, I bought, with a friend. a 4 gauge vacuum set. Years later the friend went the single cylinder route - he is a good mechanic btw - and had no need for it anymore. I now share the set with another friend, a mechanic in the yachting world. If I had known in the 80s what I know now, I would have been less impressed by the gauges and would have built the tool myself.

Looking at the design, I find the Morgan heavily overpriced and I suspect a patent that blocks competition. For a professional workshop the expense matters less than for a single individual that doesn't own a fleet of bikes. The more so if your bike doesn't need synchronisation in tens of thousands of miles as is my experience. Except for the 4 cable operated carbs that were on the first CB750s, all SOHC Fours have the carb lay out designed thus, that carbs rarely need syncing if at all. The mere fact that checking synchronisation is in the maintenance interval scheme, does not mean that resyncing will routinely be required! Far from it. In my experience I would immediately suspect another item like the ignition that needs to be adressed. But... how was Honda to know on forehand that the carbs would behave so well in real life?! If you can't foresee this, ofcourse you advise checking in the maintenance interval scheme. I have the feeling that owners of a vacuum set are a bit biased after they've spent money on it. What syncing does, is giving the bike a nice idle and that's it. Back then, nobody that I knew, would mess with the carbs and so you could achieve/restore that nice idle simply by doing the other servicing items. Then people began buying manuals where practically all 'repairs' imaginable are described unfiltered. Haynes in this respect has the better manual, stating that a single sync in the bike's lifetime (not abnormal!) does not outweigh the expense. From my experience, I can agree full heartedly. Personally I like to see people creating stuff themself.* I admire ingenuity and simplicity and would like to see more of that. The main thing with building your own sync set ofcourse is, how you can prevent fluid being sucked in the cylinders and the dampening. We could make it a contest. If you think you've built a good one, show us! Description and an accompanying video ofcourse. We'll comment until we have the perfect design. BTW, I seem to remember having heard of an even simpler device that consists of transparent tube that has four exits to the carb ports and has 3 steelballs exactly fit in it at the same distance of eachother. Purpose is to keep the three balls between marked lines. Has any of you ever seen it? Did it work?* At the moment I am trying to revive an old exhaust gas analyzer. I do not know much about electronics but I don't mind to learn. I understand its working principle now and am trying to find out if it has a defect or was a (very) bad design. If any of you has experience with this, I'm all ears.

« Last Edit: October 30, 2018, 01:17:26 pm by Deltarider »

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Bench synch method worked well on my stock K6 carbs. Used a 3-5 mm drill

Ignition issue can cause bad low lift behaviour, mixed up with badly synched carbs. I have written that several times the last months. Advancer has a play, set it in its counterclockwards position and tighten its nut. T and F will now match with case mark. If set it to the other side of the play, ignition will be advanced. I solved a long period of bad low throttle lift behavior by retarding the ignition.

Bench synch method worked well on my stock K6 carbs. Used a 3-5 mm drill

When I had the carbrack out (so far 3 times since 1980 and - let me confess - mainly to satisfy my curiosity) I synchronised by sliding a small Allen key under the slides (engine side). You have to be concentrated and take it easy. Check and doublecheck ofcourse. When checked afterwards, carbs underpressures were well within 2 cm Hg of eachother and that's well within factory specs. Now, I could have been lucky, but three times? Next time I have them on the kitchen table however, I would like to test the ball bearings method, to see how that works. The idea appeals to me: simply brilliant*. BTW, Morgan has abandoned mercury long time ago. Does any of you have a clue what fluid they use now? * If you can stand the dreary, lengthy vid, have a look here.

Morgan does not use fluid they use stainless steel sliders. Think of it as a long tube instead of a little ball. A good tool lasts a lifetime and working on a lot of different bikes I like having mine around. 750 carbs are easier to bench synch then most. When you totally break down a set of 500/550 carbs off the rack the synch adjusters have to be totally removed. Get them close and 10 minutes with the fancy easy to use tool they are done and you move on. Pretty little gadget all packed back up in its pretty case and sitting on the shelf not hurting anybody

Ball trick is fun. I have not seen that before. I guess it work on throttles too.When all throttles open exactly synchronized the incoming flow should be equal......unless there are minor leaks passing by the throttle openings that must be compensated for, which a vacuum gauge will measure correctly.

My old K6 carbs are bench synched, they have also got new throttle shaft seals. Should be fine. One more reason to get my thumbs out and do my K2 build.

It would work but your actual inHg would be off since that was calibrated to the specific gravity of Hg like Maui said. If all you are looking to do is just balance your carbs then it should work fine. If you are looking to measure the actual vacuum pressure it would be wildly off if you used ATF.

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If you made a set of manometers using ATF you would need a VERY long column if your pool of ATF was open to the air. You could use a shorter column if your pool of ATF was closed off to the atmosphere and you had a small air pocket to partially form a vacuum when the carbs were pulling on the ends of the tubes so you didn't suck ATF into your carbs. The contraption would have to always be stored upright though.

Since my bike carbs are sync, I tried it on a friend bike which need to be sync. With AFT oil, it doesn't work. The oil was going up too fast. I stoped the bike because I didn't want AFT in the carbs. Like pjlogue wrote, it probably take longer tube to work with oil.